Some varied dielectric properties of materials with the tetragonal tungsten bronze crystal structure

A variety of types of dielectric behaviour is observed in some chemically similar compounds having the crystal structure of tetragonal tungsten bronze. These include: (a) barium zirconium niobate, which, as a ferro-electric material, is unusual in having a higher than second-order transition to the para-electric state, i.e. in being a ferro-electric without a Curie point; (b) materials exemplified by barium zirconium tantalate, which has a permittivity of 90 and an unusually small temperature coefficient of permittivity over the range 25¿500°C; (c) modified PbNb2O6, which, by controlled valency modification, can be caused to display a large positive temperature coefficient of resistivity. All of these types of dielectric behaviour have potential application in electronic circuit design.